1. Field of the Invention
The present invention relates to a device that includes an array of small antennas on a mandrel capable of interfacing with biomedical devices, and more particularly ophthalmic devices, such as wearable lenses, including contact lenses, implantable lenses, including intraocular lenses (IOLs) and any other type of device comprising optical components that incorporate electronic circuits and associated antennas/antenna assemblies to enable one of one- or two-way communication with the one or more electronic components and/or power transfer.
2. Discussion of the Related Art
As electronic devices continue to be miniaturized, it is becoming increasingly more likely to create wearable or embeddable microelectronic devices for a variety of uses. Such uses include monitoring aspects of body chemistry, administering controlled dosages of medications or therapeutic agents via various mechanisms, including automatically, in response to measurements, or in response to external control signals, and augmenting the performance of organs or tissues. Examples of such devices include glucose infusion pumps, pacemakers, defibrillators, ventricular assist devices and neurostimulators. A new, particularly useful field of application is in ophthalmic wearable lenses and contact lenses. For example, a wearable lens may incorporate a lens assembly having an electronically adjustable focus to correct refractive errors and/or augment or enhance performance of the eye. In another example, either with or without adjustable focus, a wearable contact lens may incorporate electronic sensors to detect concentrations of particular chemicals in the precorneal (tear) film.
The use of embedded electronics in a lens introduces a potential requirement for communication with the electronics, for a method and device for powering and/or re-energizing the electronics, for interconnecting the electronics, for internal and external sensing and/or monitoring, and for control of the electronics and the overall function of the lens.
Often it is desirable to provide for communication to or from the embedded electronics for the purpose of control and/or data gathering. Communication of this nature should preferably be performed without direct physical connection to the lens electronics, such that the electronics may be fully sealed and to facilitate communication while the lens is in use. Hence it is desirable to couple signals to the lens electronics using near-field communication technology. Accordingly, there exists a need for an antenna structure appropriate for short-range wireless communication and capable of communicating with an optical lens assembly containing an antenna such as a soft contact lens.
Near-field communication (NFC) provides short range wireless connectivity that carry secure two-way interactions between electronic components. NFC enables communication over short distance through either inductive or capacitive coupling. This means that oscillating electric and magnetic fields are separate and power may be transferred via electric fields by capacitive coupling (electrostatic induction) between metal electrodes or via magnetic fields by inductive coupling between coils of wire. In capacitive coupling, the power is transmitted by electric fields between electrodes such as metal plates. The transmitter and receiver electrodes form a capacitor, with the intervening space as the dielectric. An alternating voltage generated by the transmitter is applied to the transmitting plate, and the oscillating electric field induces an alternating potential on the receiver plate, which allows power to be transferred. Capacitive coupling is not traditionally used in low-power applications such as the present invention because the high voltages on the electrodes required to transmit significant power may potentially be hazardous. Additionally, electric fields interact strongly with most materials, including the human body, and may possibly cause excessive electromagnetic field exposure. In inductive coupling, power is transferred between coils of wire by a magnetic field. The transmitter and receiver coils together form a transformer. The magnetic field passes through the receiving coil, which facilitates the transfer of energy from one circuit to another via the mutual inductance between the two circuits. The power transferred increases with frequency and the mutual inductance between the two coils, which depend on their geometry and the distance between them.
Antenna efficiency on-body is degraded for predominantly electric-field or “E-field” antennas. Thus, the most acceptable method of communicating and recharging a battery on-body is through inductive coupling, whereby the coil(s) of the external antenna are magnetically coupled to an antenna embedded in the ophthalmic device. With the existence of inductive structures such as antennas, antenna assemblies and/or coils appropriate for use in an optical assembly, it is desirable to provide a device that utilizes a convenient method for aligning the coil structure with an inductive coil structure for efficient near field coupling.
Embedding electronics and communication capabilities in a contact lens presents a number of general challenges. In general, it is difficult to manufacture such components directly on the lens for a number of reasons, as well as mounting and interconnecting planar devices on a non-planar surface. It is also difficult to manufacture to scale. The components to be placed on or in the lens need to be miniaturized and integrated onto just 1.5 square centimeters (assuming a lens with a 7 mm radius) of the transparent polymer forming the lens while protecting components from the liquid environment on the eye. It may also difficult to make a contact lens comfortable and safe for the wearer with the added thickness of additional components.
With respect to communication devices, specific challenges include limited antenna efficiency, which is directly related to the size or area for a coil antenna, and the number of coil turns. Although, the limit of miniaturization of electronic devices has yet to be determined, the sizes of some elements in electronics remain constrained by the rules of physics, and cannot match the miniaturization demonstrated by circuit elements. Antennas needed to radiate information remain relatively large with respect to electronics the size of a grain of salt. The size of the antenna relates to the maximum inductance achievable and the maximum voltage or current that may be transferred to the device, and differential sizing has the potential to delay or exacerbate the ability to coarse-align and fine-tune align antennas to initiate a communication link. The primary issue is that, if any antenna is small enough to include on a circuit embedded in an ophthalmic device, it may not provide sufficient power levels. The received power at the antenna must be of sufficient strength to allow for transformation to adequate supply voltage levels for the circuitry inside the ophthalmic device, when excited by a reasonable power level from an external device. The efficiency of the power transfer between the antenna coil inside the ophthalmic device and an external antenna is proportional to the operating frequency, the number of windings, the angle and the size of the two coils relative to each other, and the distance between the two coils. In some cases it may not be desirable to simply increase the power applied to the external antenna or to alter the size or number of turns. A larger size ratio between the two antennas could result in non-predictable or performance-degrading characteristics. It may be better to closely couple an equally sized, low-power external antenna. However, considering the fundamental size constraints of the internal antenna, equally sized antennas would cause the antenna coils to be extremely sensitive to alignment. Even the slightest mis-alignment of the coils may result in insufficient power. Moreover, this difficulty increases greatly when utilizing micron-sized antennas, where one antenna is embedded inside an ophthalmic device, which eliminates the possibility of any direct contact coupling methods.
Accordingly, there exists a need for providing a mechanically robust external antenna assembly that meets the requirements for functionality and performance in the volume and area of a contact lens.